It is well known for marking instruments, especially pens, to be provided with retraction mechanisms which enable the marking or writing tip to be retracted into the body during periods of non-use. Generally speaking, the known retraction mechanisms are rather complicated and are too expensive to manufacture to make it economical for them to be incorporated in so-called disposable pens which are intended to be discarded when the ink reservoir has run dry. Consequently, nearly all disposable pens available on the market have permanently exposed writing tips and are provided with removable caps adapted to be fitted over the tips. Removable caps are inconvenient because they are easily misplaced and lost.
In British patent specification No. GB 979882, there is proposed a retractable ball-point pen in which an ink reservoir tube and writing tip are advanced and retracted relative to the pen body by a plunger received in an axial bore extending through the body. The plunger includes a leaf spring at one side and a projecting tooth at the other side adapted to engage in a hole in the body to retain the plunger in its adjusted position. The plunger is of smaller diameter than the bore so that it can move laterally relative to the body for the tooth to engage and disengage the holes. Because the plunger can move from side to side, the ink tube is not firmly supported in the lateral direction, which can detract from the writing characteristics of the pen, and the retraction mechanism may itself have a floppy feeling to it.
British patent specifications No. GB 542,782 and No. GB 1,192,116 also show writing instruments in which a pencil lead or ink reservoir tube and writing tip are advanced and retracted relative to the instrument body by a plunger which moves axially of the body.